The World Wars were always going to be a bloodbath, no matter how much preparation we did. Trench warfare in WWI, plus the Nazis fortifying Europe and Japanese culture dictating that you must fight until the end were going to take many lives in order to defeat the Central and Axis powers. Civil wars tend to be pretty messy as well due many different people fighting for different things. For example, the Spanish Civil War between Spain's Republicans and Franco's Nationalists was a hodgepodge of different areas controlled by the two sides ultimately resulting in around 500,000 people killed. Korea, I would say you're right, we should have had more troops in South Korea to defend against the North and that did contribute to a higher death count. I'll also agree with you on Vietnam, as we should have never intervened there in the first place. Ho Chi Minh, if I remember correctly, actually appealed to the United States to free Vietnam from French colonization. He was no enemy of the US until we made him an enemy.